This application claims priority to German Application No. 101 25 350.8, filed May 23, 2001, herein incorporated by reference in its entirety.
1. Field of the Invention
This invention relates to a device for cooling at least one component by means of hydraulic fluid from a hydraulic circuit which has a hydraulic pump, at least one user of hydraulic energy connected to it, and a reservoir, wherein the component is connected in the hydraulic circuit between a heat exchanger and the intake side of the pump.
2. Technical Considerations
A known device is described in EP 0 889 001 A2. This document describes in very general terms a functional principle in which the drive system of a fork lift truck, for example, an electric motor and the associated electronic power actuator or an internal combustion engine is cooled by hydraulic fluid from a hydraulic steering system. The steering pump thereby performs the function of a cooling pump. The reservoir is located in a counterweight of the fork lift truck. The counterweight, on account of its considerable mass, acts as a heat exchanger (cooler). However, this document does not contain any further information on an operationally reliable realization of the principle which is advantageous in terms of the ease and cost of construction.
Therefore, it is an object of the invention to provide a device of the general type described above but which is operationally reliable and is easy and economical to manufacture.
The invention teaches that the above object can be achieved by connecting the component into a suction line that connects the tank with the pump. Between the component and the pump there is a control valve which is connected on the input side to a bypass suction line that is connected with the reservoir. In a first switched position of the control valve, the suction line is closed and the bypass suction line is open and in a second switched position of the control valve the suction line is at least partly open and the bypass suction line is closed or at least partly closed.
The invention therefore teaches the location of the component to be cooled in the area between the reservoir and the intake side of the pump so that the component can be cooled by hydraulic fluid sucked in, wherein the suction can be influenced by the position of the control valve.
At startup, for example, when both the component to be cooled as well as the hydraulic fluid are still cold, the hydraulic fluid can flow through the bypass suction line directly to the inlet side of the pump. Therefore, there is a suction pressure which is lower than when the intake is through the suction line, i.e., through the component to be cooled.
By actuating the control valve at some later time, the system can be switched to the suction line or the suction line can be added so that hydraulic fluid flows to the suction side of the pump exclusively or additionally through the component to be cooled.
It is additionally possible to act on the control valve to influence the quantity of hydraulic fluid that is used to cool the component so that even with a relatively small temperature gradient in the heat exchanger, a sufficient amount of heat can be removed from the component to be cooled.
The heat exchanger can be integrated into the reservoir. In one advantageous embodiment of the invention, however, it is also possible to connect the heat exchanger into the suction line. In that case, the cooling action of the heat exchanger can be assisted by a fan that can be turned on and off as necessary.
In an additional advantageous configuration of the invention, the heat exchanger is connected into a return line that empties into the reservoir, in which case the hydraulic fluid in the reservoir is always cooled. The above object of the invention can also be accomplished by the connection of the component into a return line that empties into the reservoir. In the return line, upstream of the component, a control valve is located to the output side of which a bypass return line (which is routed in parallel to the return line and empties into the reservoir) is connected. In a first switched position of the control valve the return line is closed and the bypass return line is open. In a second switched position of the control valve the return line is at least partly open and the bypass return line is closed or at least partly closed.
In both of the examples described above, it is possible for an operator to actuate the control valve in any manner at any time. It is advantageous, however, if the control valve can be externally controlled as a function of the temperature of the component. An electromagnetic actuator can be used for this purpose.
The quantity of hydraulic fluid that flows through the component to be cooled can be controlled if the control valve is a continuous action valve. In connection with the above-mentioned measurement of the temperature of the component to be cooled (direct or indirect measurement, e.g., by means of the temperature difference of the hydraulic fluid flowing through it), the control valve can be actuated as necessary to deliver exactly the amount of hydraulic fluid required for the cooling of the component to be cooled.
In this context, in one advantageous development of the invention, the delivery volume of the pump can be adjusted as a function of the temperature of the component.
A combination of the two embodiments of the invention described above is also possible, in which at least one component to be cooled is located in both the suction line and in the return line.